CN110700777B - System and method for flushing coal ash in coal-bed gas well by using nitrogen foam flushing fluid - Google Patents
System and method for flushing coal ash in coal-bed gas well by using nitrogen foam flushing fluid Download PDFInfo
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- CN110700777B CN110700777B CN201911005507.5A CN201911005507A CN110700777B CN 110700777 B CN110700777 B CN 110700777B CN 201911005507 A CN201911005507 A CN 201911005507A CN 110700777 B CN110700777 B CN 110700777B
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
- E21B21/14—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor using liquids and gases, e.g. foams
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/52—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning
- C09K8/528—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning inorganic depositions, e.g. sulfates or carbonates
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
- E21B21/06—Arrangements for treating drilling fluids outside the borehole
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
- E21B21/06—Arrangements for treating drilling fluids outside the borehole
- E21B21/062—Arrangements for treating drilling fluids outside the borehole by mixing components
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B21/00—Methods or apparatus for flushing boreholes, e.g. by use of exhaust air from motor
- E21B21/10—Valve arrangements in drilling-fluid circulation systems
- E21B21/106—Valve arrangements outside the borehole, e.g. kelly valves
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/166—Injecting a gaseous medium; Injecting a gaseous medium and a liquid medium
Abstract
The invention relates to a system for flushing coal ash in a coal bed gas well by using nitrogen foam flushing fluid, which comprises the following components: the system comprises a liquid preparation tank, a pump truck, a foam generator, a nitrogen making truck group, a command truck, a well control blowout gate valve, a blowout preventer, a fluid channel conversion device, a plug valve, a return discharge pipe, a return discharge liquid storage tank, a coal bed gas well shaft and a well washing operation pipe column; well control blowout gate valve is installed at coal bed gas pit shaft top, the pump truck will join in marriage the fluid reservoir through the pipeline and be connected with the foam generator, the nitrogen generator group links to each other with the foam generator through the pipeline, the command car passes through the cable and links to each other with pump truck and nitrogen generator group, the foam generator links to each other with well control blowout gate valve, preventer is installed at well control blowout gate valve top, fluid passage conversion equipment is installed at the preventer top, the plug valve is installed at fluid passage conversion equipment top, the calandria is installed at the plug valve top. The invention has the advantages of high ash fishing efficiency, less stratum filtration loss of the flushing fluid, small water consumption, strong ash carrying capacity of the flushing fluid, small damage to a reservoir and strong blockage removing capacity.
Description
Technical Field
The invention belongs to the field of oil and gas resource development, and particularly relates to a system and a method for flushing coal ash in a coal bed gas well by using nitrogen foam flushing fluid.
Background
The coal bed gas reservoir (coal rock) has low strength and joint fracture development, and the coal rock around a well bore is damaged due to drilling disturbance in the drilling process of the coal bed gas well to form a large amount of coal rock particles. Meanwhile, drainage extraction is required in the coal bed gas exploitation process, so that coal rock particles formed in the drilling process and fly ash in the coal rock are carried into a shaft. After the coal rock particles and the fly ash are gathered in a large amount in the shaft, the seepage channels of water and coal bed gas can be blocked, and the yield of the coal bed gas is reduced and even stopped. Therefore, the operation of flushing the fly ash is required periodically in the process of extracting the coal bed gas. The existing method for removing the fly ash in the coal-bed gas well mainly comprises the following steps: a clean water washing fly ash method, a mechanical fly ash salvaging method and a combination of the two fly ash salvaging methods. They mainly present the following technical difficulties and drawbacks.
(1) The method of washing fly ash with clean water. Due to the large pores of coal rock, the development of joint fractures and the small viscosity coefficient of clear water, the formation leakage is serious in the process of performing the coal ash flushing operation by utilizing clear water, circulation cannot be established, and the coal ash cannot be carried to the ground. Meanwhile, the serious leakage causes large water consumption, poor economy, low efficiency and long construction period, and also causes serious reservoir pollution.
(2) A mechanical coal ash salvage method. According to the method, a mechanical coal ash fishing tool is put into the coal bed gas well, and the pipe column is continuously lifted down to carry the coal ash in the shaft to the ground. The pipe string pulling speed is slow, so that the efficiency of the mechanical fly ash salvaging method is low, the salvaging is not thorough, the workload is large, and the economical efficiency is poor.
(3) The mechanical fishing and the clean water cleaning are combined to fish the fly ash. The method generally comprises the steps of mechanically fishing the fly ash and then flushing the fly ash by using clear water. Although both methods can improve the efficiency of fly ash removal, the disadvantages and shortcomings of both methods cannot be essentially overcome.
Based on the technical background, the invention is needed to provide a method for flushing coal ash in a coal bed gas well by using nitrogen foam, so that the coal ash salvage efficiency of the coal bed gas well is improved, and the water consumption and the near-well stratum pollution are reduced.
Disclosure of Invention
The invention provides a method for washing coal ash in a coal bed gas well by using nitrogen foam well washing liquid, aiming at the defects of serious stratum leakage, large water consumption, poor economy, low efficiency (poor ash carrying capacity), long construction period, serious reservoir pollution and incomplete ash fishing existing in the existing methods for washing the coal ash by using clean water, mechanically fishing the coal ash and fishing the coal ash by combining the clean water and the mechanically fishing the coal ash.
In order to achieve the purpose, the invention adopts the following technical scheme:
utilize nitrogen gas foam well-flushing liquid to wash system of fly ash in coal bed gas well includes: the system comprises a liquid preparation tank, a pump truck, a foam generator, a nitrogen making truck group, a command truck, a well control blowout gate valve, a blowout preventer, a fluid channel conversion device, a plug valve, a return discharge pipe, a return discharge liquid storage tank, a coal bed gas well shaft and a well washing operation pipe column; wherein: the coal bed gas shaft is a vertical shaft, the top of the coal bed gas shaft is provided with a well control blowout gate valve, the bottom of the coal bed gas shaft is positioned in a coal bed gas reservoir, and fly ash is accumulated in the coal bed gas shaft at the middle lower part; the pump truck is connected with the foam generator through a pipeline, the nitrogen making truck group is connected with the foam generator through a pipeline, the command truck is connected with the pump truck and the nitrogen making truck group through a cable, the foam generator is connected with the well control blowout gate valve, the top of the well control blowout gate valve is provided with the blowout preventer, the top of the blowout preventer is provided with the fluid channel conversion device, the top of the fluid channel conversion device is provided with the plug valve, and the top of the plug valve is provided with the return exhaust pipe.
The method for flushing the fly ash in the coal bed gas well by using the nitrogen foam flushing liquid comprises the following steps:
s1, preparing a shaft
S2, descending a well washing operation pipe column to the top of the ash flushing surface
S3 preparation of well-flushing liquid
S4, ground equipment preparation and process connection
S5, ground process pressure test
S6, establishing circulation of well-flushing liquid
S7, continuously washing the pipe column of the well-flushing operation to the designed depth
And S8, degassing clear water and pulling out the operation pipe column.
Compared with the prior art, the invention has the following beneficial effects: the efficiency of fishing ash is high, the stratum filtration loss of the flushing fluid is less, the water consumption is low, the flushing fluid has strong ash carrying capacity, and the construction period can be shortened by more than 50%; the coal ash around the shaft can be carried into the shaft by utilizing negative pressure, so that the permeability of the stratum around the shaft is increased, the damage to a reservoir stratum is small, and the blockage removing capability is strong; the economic benefit is high, and the input and output ratio can be improved by more than 50% compared with the traditional ash fishing method.
Drawings
FIG. 1 is a schematic diagram of a method for flushing fly ash in a coal bed gas well using a nitrogen foam flushing fluid;
in the figure: 1. preparing a liquid tank; 2. a pump truck; 3. a foam generator; 4. a nitrogen making vehicle set; 5. a command vehicle; 6. a pipeline; 7. a cable; 8. a well-controlled blowout gate valve; 9. a blowout preventer; 10. a fluid passage switching device; 11. a plug valve; 12. a return pipe; 13. a return liquid storage tank; 14. a well-flushing operation tubular column; 15. a coal bed gas wellbore; 16. nitrogen foam flushing fluid; 17. fly ash; 18. and (4) coal bed gas reservoir.
Detailed Description
As shown in fig. 1, a schematic diagram of a system construction operation for flushing coal ash in a coal-bed gas well by using a nitrogen foam flushing fluid includes: the system comprises a liquid preparation tank 1, a pump truck 2, a foam generator 3, a nitrogen making truck group 4, a command truck 5, a well control blowout gate valve 8, a blowout preventer 9, a fluid channel conversion device 10, a plug valve 11, a return pipe 12, a return liquid storage tank 13, a coal bed gas well shaft 15 and a well washing operation pipe column 14; the coal bed gas shaft 15 is a vertical shaft, and the top of the coal bed gas shaft is provided with a well control blowout gate valve which is used for liquid in the coal bed gas reservoir 18 in the blowout well-washing operation process; the bottom of the coal bed gas well barrel is positioned in a coal bed gas reservoir 18, and fly ash 17 is accumulated in a coal bed gas well barrel at the middle lower part; injecting nitrogen foam flushing liquid 16 from an annular space between the flushing operation pipe column 14 and the coal bed gas shaft 15, discharging the nitrogen foam flushing liquid from the flushing operation pipe column 14, and carrying the coal ash in the coal bed gas shaft to the ground so as to achieve the purpose of flushing the coal bed gas shaft; the pump truck 2 is used for connecting the liquid preparation tank 1 with the foam generator 3 through a pipeline 6 and pumping the well-flushing liquid in the liquid preparation tank into the foam generator; the nitrogen making truck group 4 is connected with the foam generator through a pipeline 6 and is used for injecting nitrogen into the foam generator; the command vehicle 5 is connected with the pump truck 2 and the nitrogen making truck group 4 through a cable 7 and is used for controlling the well washing construction operation parameters of the nitrogen foam well washing liquid; the foam generator 3 is connected with a well control blowout gate valve 8 and is used for injecting nitrogen foam well flushing liquid into an annular space between the coal bed gas shaft and the well flushing operation tubular column; a blowout preventer 9 is arranged at the top of the well control blowout gate valve 8 and used for controlling blowout possibly occurring in the well washing operation process; the top of the blowout preventer is provided with a fluid channel switching device 10 for switching a flow channel of the nitrogen foam flushing fluid; the top of the fluid channel conversion device 10 is provided with a plug valve 11 for controlling the flow of the nitrogen foam flushing liquid when the flushing operation pipe column is connected with a single pipe; the top of the plug valve 11 is provided with a return pipe 12 for conveying liquid returned from the coal bed gas reservoir in the well washing operation process to a return liquid storage tank 13.
A method for flushing coal ash in a coal bed gas well by using nitrogen foam flushing fluid comprises the following steps:
s1, preparing a shaft
Determining a coal bed gas well needing coal ash washing, treating a well site, and conveniently taking out mechanical equipment for operation of an original production pipe column in a coal bed gas shaft to enter the well site; the original production pipe column in the coal bed gas shaft is taken out, and then a drifting operation tool is put in to carry out drifting operation, so that smoothness of the coal bed gas shaft is ensured, and the well washing operation pipe column can be smoothly put in; after the drifting operation is finished, carrying out liquid pressure test on the coal bed gas shaft, and installing a wellhead device required for flushing a well by using nitrogen foam flushing fluid after the pressure test is qualified;
s2, descending a well washing operation pipe column to the top of the ash flushing surface
A well washing operation pipe column is put into the coal bed gas shaft until the well washing operation pipe column cannot be put into the coal bed gas shaft continuously by means of self weight, and the depth position corresponding to the well washing operation pipe column is the fly ash surface position; after the position of the fly ash surface is determined, lifting the well washing operation pipe column to a position 10m above the fly ash surface;
s3 preparation of well-flushing liquid
Calculating the volume of the coal bed gas well cylinder according to the inner diameter of the coal bed gas well cylinder and the burial depth of the fly ash surface, preparing clear water with qualified quality according to the volume of 5-10 times of the volume of the coal bed gas well cylinder, and referring to the requirements of class I water in underground water quality standard GB/T14848-93 for the quality requirements of the clear water; injecting prepared qualified clear water into a liquid preparation tank with a clean inner wall, adding potassium chloride solid accounting for 1% -2% of the mass of the clear water into the liquid preparation tank after the clear water is mixed fully, dissolving the potassium chloride in the clear water completely, enabling no solid potassium chloride to be deposited at the bottom of the liquid preparation tank, sequentially adding a foaming agent accounting for 0.5% of the mass of the clear water and a foam stabilizer accounting for 2% of the mass of the clear water, not stirring, standing for more than 6 hours, detecting the quality of a mixture water solution, completing the preparation of the well-flushing liquid after the detection is qualified, and allowing the well-flushing liquid to be used in later well-flushing operation;
s4, ground equipment preparation and process connection
According to the construction operation requirement of flushing the fly ash in the coal-bed gas well by using the nitrogen foam flushing fluid, the ground equipment needing to be prepared comprises: the system comprises a pump truck, a nitrogen making truck group, a foam generator, a command truck, a plug valve, a well control blowout gate valve, a blowout preventer, a pipeline, a fluid channel conversion device, a liquid distribution tank, a return discharge pipe, a return discharge liquid storage tank and a cable; and connecting the devices in the following order: one end of the pump truck is connected with the fluid preparation tank through a pipeline, the other end of the pump truck is connected with the foam generator, and the well washing fluid in the fluid preparation tank is pumped into the foam generator; the foam generator is of a three-way structure, and a first interface is connected with the nitrogen making truck group and used for receiving nitrogen pumped by the nitrogen making truck group; the second interface is connected with the pump truck group and used for receiving the well-flushing liquid pumped by the pump truck; the third interface of the foam generator is connected with the first interface of the well control blowout gate valve, and the well control blowout gate valve is a three-way component; a second interface at the bottom of the well control blowout gate valve is connected with the mouth of the coal bed gas well and used for injecting the generated nitrogen foam well washing liquid into a coal bed gas shaft; the third interface at the top of the well control blowout gate valve is connected with the blowout preventer; the top of the blowout preventer is provided with a fluid channel switching device; the top of the fluid channel switching device is provided with a plug valve; the top of the plug valve is provided with a return discharge pipe which is connected with a return discharge liquid storage tank; the command vehicle is connected with the pump truck and the nitrogen making truck group through cables to control the construction parameters of the well washing operation, so that the ground flow connection is completed;
s5, ground process pressure test
Closing a wellhead gate valve, limiting the pressure test fluid to flow into a coal bed gas shaft, starting a pump truck to pressurize until the minimum rated working pressure of each part of the ground flow is reached, maintaining the pressure for 5 minutes without puncture, and considering the pressure test to be qualified;
s6, establishing circulation of well-flushing liquid
Opening a wellhead gate valve, and injecting the prepared flushing fluid and nitrogen into a foam generator by using a pump truck to form nitrogen foam flushing fluid; injecting the nitrogen foam flushing fluid through an annulus between the flushing operation pipe column and the coal bed gas shaft, and returning the nitrogen foam flushing fluid out of the flushing operation pipe column; continuously injecting nitrogen foam flushing fluid to a backflow pipe orifice of a flushing operation pipe column to stably discharge liquid for 2-3 minutes; controlling the density of the generated nitrogen foam flushing fluid to be 5-10% lower than the formation pressure gradient by adjusting the injection ratio of nitrogen and flushing fluid;
s7, continuously washing the pipe column of the well-flushing operation to the designed depth
A plug valve is arranged on a pipe column joint before the pipe column is put into the well-flushing operation and is used for controlling the outflow of nitrogen foam well-flushing liquid in the pipe column; continuously injecting nitrogen foam flushing fluid, slowly descending into a flushing operation pipe column at a constant speed, and observing a derrick weight suspension table at any time to determine whether the bottom surface of the flushing operation pipe column is in contact with the ash surface; if the hanging weight is reduced by 5-10kN, the pressure of the pump truck is increased by 1-2MPa, and the liquid outlet quantity of the well head is reduced, stopping running into the well washing operation pipe column, continuously injecting nitrogen foam well washing liquid, and upwards lifting the well washing operation pipe column at a constant speed for 5-10 m; continuously and circularly injecting the nitrogen foam flushing fluid, and gradually reducing the density of the nitrogen foam flushing fluid to 60-80% of the density of the initial nitrogen foam flushing fluid to form negative pressure, so that negative pressure blockage removal can be realized to the maximum extent; then gradually increasing the density of the nitrogen foam flushing fluid to the initial density of the nitrogen foam flushing fluid, and improving the rock carrying capacity; injecting nitrogen foam flushing fluid to 2-3 times of the volume of the coal bed gas shaft, recovering the pump truck pressure and the outlet fluid of the well mouth to be normal, and slowly descending the flushing operation pipe column at a constant speed; when a single pipe column is connected with a well washing operation, the plug valve needs to be closed, and the plug valve is opened after the completion; repeating the process until the well washing operation pipe column is lowered to the designed depth; collecting the flowback liquid every 5 minutes, standing for 30 minutes, analyzing the shape, color, content and components of the solid sediment until the quality of the liquid at an inlet and an outlet meets the design requirements, and finishing the coal bed gas well coal ash washing operation;
s8 clear water degassing and pulling out operation pipe column
After the coal ash washing operation is finished, stopping injecting the nitrogen foam well washing liquid, then injecting clear water with the volume of 1.5-2 times of the volume of the coal bed gas well cylinder into the well cylinder through a well washing operation pipe column and the coal bed gas well cylinder annulus, completely displacing the foam well washing liquid in the coal bed gas well cylinder to the ground, and closing a pump truck; pulling out the well washing operation pipe columns at the pulling-out speed of not more than 15 pipes/hour until all the well washing operation pipe columns are pulled out; and (5) disassembling the ground flow.
Therefore, the method can effectively solve the defects of serious stratum loss, large water consumption, poor economy, low efficiency (poor ash carrying capacity), long construction period, serious reservoir pollution and incomplete ash fishing in the methods of washing the fly ash by using clear water, mechanically fishing the fly ash and fishing the fly ash by combining the clear water and the mechanically fished fly ash, and has the advantages of clear operation steps and clear parameter value range.
Claims (1)
1. A method for flushing coal ash in a coal bed gas well by using nitrogen foam flushing fluid is characterized by comprising the following steps:
s1, preparing a shaft
S2, descending a well washing operation pipe column to the top of the ash flushing surface
S3 preparation of well-flushing liquid
S4, ground equipment preparation and process connection
S5, ground process pressure test
S6, establishing circulation of well-flushing liquid
S7, continuously washing the pipe column of the well-flushing operation to the designed depth
S8, degassing clear water and pulling out the operation pipe column;
the specific method of step S1 is as follows: determining a coal bed gas well needing coal ash washing, treating a well site, and conveniently taking out mechanical equipment for operation of an original production pipe column in a coal bed gas shaft to enter the well site; the original production pipe column in the coal bed gas shaft is taken out, and then a drifting operation tool is put in to carry out drifting operation, so that smoothness of the coal bed gas shaft is ensured, and the well washing operation pipe column can be smoothly put in; after the drifting operation is finished, carrying out liquid pressure test on the coal bed gas shaft, and installing a wellhead device required for flushing a well by using nitrogen foam flushing fluid after the pressure test is qualified;
the specific method of step S2 is as follows: a well washing operation pipe column is put into the coal bed gas shaft until the well washing operation pipe column cannot be put into the coal bed gas shaft continuously by means of self weight, and the depth position corresponding to the well washing operation pipe column is the fly ash surface position; after the position of the fly ash surface is determined, lifting the well washing operation pipe column to a position 10m above the fly ash surface;
the specific method of step S3 is as follows: calculating the volume of the coal bed gas well cylinder according to the inner diameter of the coal bed gas well cylinder and the burial depth of the fly ash surface, preparing clear water with qualified quality according to the volume of 5-10 times of the volume of the coal bed gas well cylinder, and referring to the requirements of class I water in underground water quality standard GB/T14848-93 for the quality requirements of the clear water; injecting prepared qualified clear water into a liquid preparation tank with a clean inner wall, adding 1-2% of potassium chloride solid by mass of clear water into the liquid preparation tank, fully stirring to enable the potassium chloride to be completely dissolved in the clear water, enabling no solid potassium chloride to be deposited at the bottom of the liquid preparation tank, sequentially adding a foaming agent by mass of 0.5% of the clear water and a foam stabilizer by mass of 2% of the clear water, not stirring, standing for more than 6 hours, detecting the quality of a mixture water solution, completing the preparation of a well-flushing liquid after the detection is qualified, and allowing the well-flushing liquid to be used in later well-flushing operation;
the specific method of step S4 is as follows: according to the construction operation requirement of flushing the fly ash in the coal-bed gas well by using the nitrogen foam flushing fluid, the ground equipment needing to be prepared comprises: the system comprises a pump truck, a nitrogen making truck group, a foam generator, a command truck, a plug valve, a well control blowout gate valve, a blowout preventer, a pipeline, a fluid channel conversion device, a liquid distribution tank, a return discharge pipe, a return discharge liquid storage tank and a cable; and connecting the devices in the following order: one end of the pump truck is connected with the fluid preparation tank through a pipeline, the other end of the pump truck is connected with the foam generator, and the well washing fluid in the fluid preparation tank is pumped into the foam generator; the foam generator is of a three-way structure, and a first interface is connected with the nitrogen making truck group and used for receiving nitrogen pumped by the nitrogen making truck group; the second interface is connected with the pump truck group and used for receiving the well-flushing liquid pumped by the pump truck; the third interface of the foam generator is connected with the first interface of the well control blowout gate valve, and the well control blowout gate valve is a three-way component; a second interface at the bottom of the well control blowout gate valve is connected with the mouth of the coal bed gas well and used for injecting the generated nitrogen foam well washing liquid into a coal bed gas shaft; the third interface at the top of the well control blowout gate valve is connected with the blowout preventer; the top of the blowout preventer is provided with a fluid channel switching device; the top of the fluid channel switching device is provided with a plug valve; the top of the plug valve is provided with a return discharge pipe which is connected with a return discharge liquid storage tank; the command vehicle is connected with the pump truck and the nitrogen making truck group through cables to control the construction parameters of the well washing operation, so that the ground flow connection is completed;
the specific method of step S5 is as follows: closing a wellhead gate valve, limiting the pressure test fluid to flow into a coal bed gas shaft, starting a pump truck to pressurize until the minimum rated working pressure of each part of the ground flow is reached, maintaining the pressure for 5 minutes without puncture, and considering the pressure test to be qualified;
the specific method of step S6 is as follows: opening a wellhead gate valve, and injecting the prepared flushing fluid and nitrogen into a foam generator by using a pump truck to form nitrogen foam flushing fluid; injecting the nitrogen foam flushing fluid through an annulus between the flushing operation pipe column and the coal bed gas shaft, and returning the nitrogen foam flushing fluid out of the flushing operation pipe column; continuously injecting nitrogen foam flushing fluid to a backflow pipe orifice of a flushing operation pipe column to stably discharge liquid for 2-3 minutes; controlling the density of the generated nitrogen foam flushing fluid to be 5-10% lower than the formation pressure gradient by adjusting the injection ratio of nitrogen and flushing fluid;
the specific method of step S7 is as follows: a plug valve is arranged on a pipe column joint before the pipe column is put into the well-flushing operation and is used for controlling the outflow of nitrogen foam well-flushing liquid in the pipe column; continuously injecting nitrogen foam flushing fluid, slowly descending into a flushing operation pipe column at a constant speed, and observing a derrick weight suspension table at any time to determine whether the bottom surface of the flushing operation pipe column is in contact with the ash surface; if the hanging weight is reduced by 5-10kN, the pressure of the pump truck is increased by 1-2MPa, and the liquid outlet quantity of the well head is reduced, stopping running into the well washing operation pipe column, continuously injecting nitrogen foam well washing liquid, and upwards lifting the well washing operation pipe column at a constant speed for 5-10 m; continuously and circularly injecting the nitrogen foam flushing fluid, and gradually reducing the density of the nitrogen foam flushing fluid to 60-80% of the density of the initial nitrogen foam flushing fluid to form negative pressure, so that negative pressure blockage removal can be realized to the maximum extent; then gradually increasing the density of the nitrogen foam flushing fluid to the initial density of the nitrogen foam flushing fluid, and improving the rock carrying capacity; injecting nitrogen foam flushing fluid to 2-3 times of the volume of the coal bed gas shaft, recovering the pump truck pressure and the outlet fluid of the well mouth to be normal, and slowly descending the flushing operation pipe column at a constant speed; when a single pipe column is connected with a well washing operation, the plug valve needs to be closed, and the plug valve is opened after the completion; repeating the process until the well washing operation pipe column is lowered to the designed depth; collecting the flowback liquid every 5 minutes, standing for 30 minutes, analyzing the shape, color, content and components of the solid sediment until the quality of the liquid at an inlet and an outlet meets the design requirements, and finishing the coal bed gas well coal ash washing operation;
the specific method of step S8 is as follows: after the coal ash washing operation is finished, stopping injecting the nitrogen foam well washing liquid, then injecting clear water with the volume of 1.5-2 times of the volume of the coal bed gas well cylinder into the well cylinder through a well washing operation pipe column and the coal bed gas well cylinder annulus, completely displacing the foam well washing liquid in the coal bed gas well cylinder to the ground, and closing a pump truck; pulling out the well washing operation pipe columns at the pulling-out speed of not more than 15 pipes/hour until all the well washing operation pipe columns are pulled out; and (5) disassembling the ground flow.
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